1. Field of the Invention
The present invention relates generally to semiconductor devices and methods of fabricating the same, and particularly to semiconductor devices having an interconnection structure providing a plug for example of tungsten in a contact hole between multilayer interconnections for electrical conduction and methods of fabricating the same.
2. Description of the Background Art
A method of providing a tungsten plug in a conventional semiconductor device is described for example in Japanese Patent Laying-Open No. 11-330241.
As described in Japanese Patent Laying-Open No. 11-330241, initially at a substrate provided with a contact hole a barrier metal is provided and thereon tungsten is provided in a film. Subsequently the tungsten is etched back to form a plug. Note that when the tungsten is being overetched the barrier metal and fluorine supplied from an etchant gas react with each other and adhere on the barrier metal, forming a reaction product. Subsequently, the substrate remains in the same chamber, rather than being transported to a different chamber, and is processed with an O2 plasma. The processing with the plasma oxidizes a surface of the barrier metal, including a region corresponding to the reaction product, to provide an oxide film layer. As a result, short circuit of a pattern on the barrier metal, or the like can be prevented.
As disclosed in Japanese Patent Laying-Open No. 11-330241, however, an oxide film layer and a reaction product layer exist between a tungsten plug and an overlying interconnection. As such, the reaction product can hardly be controlled in thickness. This results in an unstable electric resistance value between the tungsten plug and the overlying interconnection.
Furthermore, as disclosed in Japanese Patent Laying-Open No. 11-330241, the processing chamber in which the tungsten is etched back is also used for a subsequent ashing step, and an oxide gas is introduced into an etching-back chamber for the ashing step. The gas oxidizes a reaction product deposited in the processing chamber, producing foreign matters. Furthermore, changing the atmosphere in the chamber between the etching-back and ashing steps entails a period of time before the atmosphere stabilizes, which is an obstacle to constant production.